Calcium Ion Regulates the Release of Lipase of Fusarium oxysporum

Abstract

The lipase production of a plant pathogenic fungus, Fusarium oxysporum f. sp. lini SUF 402, was induced by fat as the carbon source, and its release was stimulated by the infusion of intracellular free calcium ion with a calcium ionophore, A23187. N-(6-Aminohexyl)-5-chloro-1-naphthalenesulfonamide (W-7, a calmodulin inhibitor) and 1-[N, O-bis(5-isoquinolinesulfonyl)-N-methyl-L-tyrosyl]-4-phenylpiperazine (KN-62, a Ca²⁺/calmodulin dependent protein kinase II inhibitor) reduced the extracellular release of lipase in vivo. 1-(5-Isoquinolinylsulfonyl)-2-methylpiperazine (H-7, a protein kinase C inhibitor) did not have this ability. After K₂H³²PO₄, had been incorporated into the cells, they were treated with W-7 or KN-62 and stimulated by Ca²⁺ ionophore. On SDS-PAGE of intracellular proteins followed by autoradiography, W-7- and KN-62-treated cells showed inhibition of the incorporation of ³²Pi into the 20 kDa protein resulting from Ca²⁺ stimulation. F. oxysporum had calmodulin (CaM)-dependent protein kinase activity in the cytoplasmic fraction and had the ability to phosphorylate of syntide 2, a specific substrate of CaM kinase II. The partially purified CaM-dependent protein kinase was inhibited by 10 μM KN-62 in vitro. Increase of the intracellular Ca²⁺ concentration of F. oxysporum activated CaM and CaM-dependent protein kinase, resulting in the extracellular lipase release. These results suggest the existence of a Ca²⁺ signalling system in F. oxysporum like those observed in higher eucaryotes.